Many varieties of coating compositions have been used in the past based on various polymeric materials. These coatings are either solvent borne or water borne. Solvent borne coatings are disadvantageous in that large amounts of volatile organic solvents are present. These solvents may be costly and hazardous. Water borne coatings are also disadvantageous in that they are not continuous and have been found to contain more pinholes and voids than the solvent borne coatings. Furthermore, the cure of these coatings often requires excessive input of thermal energy.
The search for an essentially solvent-free, non-polluting, low energy-utilizing coating process has led to the use of radiation curable coating systems. However, the hardness and adhesion of the cured film to the desired substrate has been poor because of the inherently low temperatures utilized in radiation curing of the composition.
The use of nitrile barrier latex coatings are known in the art. Representative examples of nitrile latex coating compositions and their preparation include those disclosed in U.S. Pat. Nos. 4,379,875 and 4,374,948. These patents teach that the nitrile latex coatings are thermally cured. Thermally cured nitrile latex coating processes require a high thermal energy input. Further, thermally cured coating compositions generally are 5-15 mils thick for corrosion resistant systems.
The use of photoinitiators is taught by several U.S. patents. U.S. Pat. No. 3,090,664 for instance, is directed toward a process for forming graft copolymers comprising unsaturated organic acids and nitrogen-containing polymer structure such as fibers, fabrics and films. The polymer structure is impregnated with the polymerizable organic acid and then exposed to ultraviolet light. Photoinitiators are optionally employed with or without a solvent and are contacted by the polymer substrate either before or after impregnation.
U.S. Pat. No. 3,943,103 is directed toward radiation curable polymer compositions comprising vinyl acetate and a polyfunctional reactive compound containing at least two radiation curable polymerizable olefin units.
U.S. Pat. No. 3,977,954 is directed toward a method for the formation of graft copolymers on polymeric substrates. The method includes the steps of depositing a wetting agent onto the surface of the substrate; then contacting the surface with an unhalogenated vinyl monomer vapor and a vapor of photosensitive compound in the presence of light energy.
In none of these instances has the art recognized the use of a high nitrile content copolymer with a photoinitiator and a polymerizable solvent to form a coating composition.